Add pv optimization tutorial

Signed-off-by: Matthias Wende <matthias.wende@frequenz.com>

docs/tutorials/pv_optimization.md

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+# Optimizing PV production
+
+## Introduction
+
+Before we start it's assumed that you have finished the first [tutorial](./getting_started.md)
+
+In this tutorial you will write an application that optimizes the energy produced from a PV system with
+Battery for self consumption.
+In order to do so you need to measure the power that flows through the
+[grid connection point](../../intro/glossary/#grid) to determine excess power.
+
+## Measure the excess power
+
+When using the term excess power what we actually mean is the consumer excess power, that is the power that
+flows from the PV system into the grid.
+
+!!! note
+
+    We are using the [passive sign convention](../../intro/glossary/#passive-sign-convention) and thus power
+    flowing from PV is negative and consumed power is positive.
+
+We want to measure the excess power. In order to do so you can use the SDK's data pipeline and especially
+the pre defined
+[consumer](../../reference/frequenz/sdk/timeseries/logical_meter/#frequenz.sdk.timeseries.logical_meter.LogicalMeter.consumer_power)
+and
+[producer power](../../reference/frequenz/sdk/timeseries/logical_meter/#frequenz.sdk.timeseries.logical_meter.LogicalMeter.producer_power)
+formulas.
+
+```python
+async def run() -> None:
+    ... # (1)!
+
+    # negative means feed-in power due to the negative sign convention
+    consumer_excess_power_engine = (
+        microgrid.logical_meter().producer_power
+        + microgrid.logical_meter().consumer_power
+    ).build("excess_power") # (2)!
+    cons_excess_power_recv = consumer_excess_power_engine.new_receiver() # (3)!
+```
+
+1. The initialization code as explained in the Getting Started tutorial.
+2. Construct the consumer excess power by summing up consumer and producer power each of which having
+opposite signs due to the sign convention. This returns a formula engine.
+3. Request a receiver from the formula engine which will be used to consume the stream.
+
+## Control the Battery
+
+Now, with the constructed excess power data stream use a
+[battery pool](../../reference/frequenz/sdk/timeseries/battery_pool/) to implement control logic.
+
+```python
+    ...
+
+    battery_pool = microgrid.battery_pool() # (1)!
+
+    async for cons_excess_power in cons_excess_power_recv: # (2)!
+        cons_excess_power = cons_excess_power.value # (3)!
+        if cons_excess_power is None: # (4)!
+            continue
+        if cons_excess_power <= Power.zero(): # (5)!
+            await battery_pool.charge(-cons_excess_power)
+        elif cons_excess_power > Power.zero():
+            await battery_pool.discharge(cons_excess_power)
+```
+
+1. Get an instance of the battery pool.
+2. Iterate asynchronously over the constructed consumer excess power stream.
+3. Get the `Quantity` from the received `Sample`.
+4. Do nothing if we didn't receive new data.
+5. Charge the battery if there is excess power and discharge otherwise.
+
+And that's all you need to know to write the simple application for storing PV excess power in a battery.
+
+## Full example
+
+Here is a copy & paste friendly version
+
+```python
+import asyncio
+
+from datetime import timedelta
+from frequenz.sdk import microgrid
+from frequenz.sdk.actor import ResamplerConfig
+from frequenz.sdk.timeseries import Power
+
+async def run() -> None:
+    # This points to the default Frequenz microgrid sandbox
+    microgrid_host = "microgrid.sandbox.api.frequenz.io"
+    microgrid_port = 62060
+
+    # Initialize the microgrid
+    await microgrid.initialize(
+        microgrid_host,
+        microgrid_port,
+        ResamplerConfig(resampling_period=timedelta(seconds=1)),
+    )
+
+    # negative means feed-in power due to the negative sign convention
+    consumer_excess_power_engine = (
+        microgrid.logical_meter().producer_power
+        + microgrid.logical_meter().consumer_power
+    ).build("excess_power") # (2)!
+    cons_excess_power_recv = consumer_excess_power_engine.new_receiver() # (3)!
+
+    battery_pool = microgrid.battery_pool() # (1)!
+
+    async for cons_excess_power in cons_excess_power_recv: # (2)!
+        cons_excess_power = cons_excess_power.value # (3)!
+        if cons_excess_power is None: # (4)!
+            continue
+        if cons_excess_power <= Power.zero(): # (5)!
+            await battery_pool.charge(-cons_excess_power)
+        elif cons_excess_power > Power.zero():
+            await battery_pool.discharge(discharge_power)
+
+def main() -> None:
+    asyncio.run(run())
+
+if __name__ == "__main__":
+    main()
+```
+
+## Further reading
+
+To create more advanced applications it is suggested to read the [actors](../../intro/actors/) documentation.